Actinomycetes comprise a family of bacteria that are abundant in soil and have generated significant commercial and scientific interest as a result of the large number of therapeutically useful antibiotics, antifungals, anticancer and cholesterol-lowering agents, produced as secondary metabolites by these bacteria. Many actinomycetes, particularly those of the Streptomyces genus, have been extensively studied because of their ability to produce a notable diversity of biologically active metabolites. The intensive search for new natural products has led to the identification of new species of bacteria and the creation of improved strains.
Polyene polyketides are a group of natural products produced by actinomycetes that have generated significant commercial interest. For example Sakuda et al, 1996 J. of Chem. Soc., Perkin trans. 1, 2315-19; and Sakuda et al., Tetrahedron Letters, Vol 35, No.16, 2777-2789 (1995) disclose the linear polyene linearmycin A produced by a Streptomyces sp. Sakuda et al. report that linearmycin A has shown both antifungal and antibacterial activity. Pawlak et al. J. of Antibiotics, Vol. XXXIII No. 9, 989-997 disclose the polyene macrolide lienomycin produced by Actinomyces diastatochromogenes. Pawlak et al. report that lienomycin has shown antifungal, antibacterial and anti-tumor activity. Antifungal activity of polyene macrolides has also been correlated with hyperchlesterolemic effect (C. P. Schaffner, Polyene Microlides in Clinical Practice, in Macrolide Antibiotics: Chemistry, biology and practice, S. Omura, ed. Academic Press (1984), p. 491; C. P. Schaffner and H. W. Gordon, Proc Natl. Acad. Sci. U.S.A. 61, 36 (1968)).
Polyketides have carbon chain backbones formed of two-carbon units through a series of condensations reactions and subsequent modifications. Type I polyketides are synthesized in nature by modular polyketide synthase (PKS) enzymes having a set of separate catalytic active sites for each cycle of carbon chain elongation and modification. Because of the multimodular nature of PKS proteins, much is known of the specificity and mechanism of the biosynthesis of polyketides.
Although many biologically active compounds have been identified, there remains the need to obtain novel naturally occurring compounds with enhanced properties. Current methods of obtaining such compounds include screening of natural isolates and chemical modification of existing compounds, both of which are costly and time consuming. Current screening methods are based on general biological properties of the compound, which require prior knowledge of the structure of the molecules. Methods for chemically modifying known active compounds exist, but still suffer from practical limitations as to the type of compounds obtainable.
Thus, there exists a considerable need to obtain pharmaceutically active compounds in a cost-effective manner and with high yield. The present invention solves these problems by providing improved strains of Streptomyces aizunensis capable of producing potent new therapeutic compounds, as well as reagents (e.g. polynucleotides, vectors comprising the polynucleotides and host cells comprising the vectors) and methods to generate novel compounds by de novo biosynthesis rather than by chemical synthesis.